How to Fix Access Denied for Operation AWS CloudFront Distribution (403 Forbidden)

Understanding the 'Access Denied for Operation AWS CloudFront Distribution' Error

When operating AWS CloudFront as a Content Delivery Network (CDN) in front of an Amazon S3 bucket, encountering a 403 Forbidden or Access Denied error is one of the most common issues DevOps and Site Reliability Engineers face. AWS S3 does not explicitly return a 404 Not Found for missing objects if the requester lacks the s3:ListBucket permission. Instead, it returns a 403 Access Denied. This obfuscation often leads engineers down the wrong troubleshooting path.

This guide explores the architectural nuances of CloudFront-to-S3 integrations and provides a definitive, step-by-step workflow to resolve these access control issues.

The Anatomy of the Request

To understand why you are receiving an aws cloudfront s3 access denied error, we must trace the request lifecycle:

1. Client to Edge Location: The user's browser requests a cached asset from the nearest CloudFront edge location.
2. WAF Evaluation (Optional): If AWS WAF is attached, the request is evaluated against Web ACLs.
3. Cache Evaluation: CloudFront checks its cache. If it's a miss, it forwards the request to the Origin.
4. Origin Request: CloudFront signs the request using OAC (Origin Access Control) or OAI (Origin Access Identity) and attempts to retrieve the object from S3.
5. S3 Evaluation: S3 evaluates bucket policies, KMS key policies, and object ownership.

A failure at steps 2, 4, or 5 will result in a 403 error.

Step 1: Diagnose the Root Cause

Before modifying infrastructure, identify exactly which layer is throwing the 403.

A. Verify with cURL

Use curl to inspect the response headers. CloudFront provides debugging headers that indicate whether the error came from the edge or the origin.

curl -I https://d111111abcdef8.cloudfront.net/index.html

Look for the x-cache header:

• x-cache: Error from cloudfront: The error was generated by CloudFront (e.g., WAF blocked it, Geo-restriction, or missing alternate domain name).
• x-cache: Miss from cloudfront: The request reached S3, and S3 denied the request. This points directly to S3 Bucket Policies, IAM, or KMS.

B. Enable Standard Logging

If the issue is intermittent, enable CloudFront standard logging to an S3 bucket or query the logs using Amazon Athena to identify the sc-status (HTTP status code) and x-edge-detailed-result-type.

Step 2: Fix S3 Bucket Policies (OAC vs OAI)

AWS strongly recommends migrating from Origin Access Identity (OAI) to Origin Access Control (OAC). OAC provides better security, supports AWS KMS encrypted buckets, and works across all AWS regions.

The Solution for OAC

If you are using OAC, your S3 bucket policy must explicitly grant the s3:GetObject permission to the CloudFront service principal, conditional upon the specific distribution ARN.

1. Open the Amazon S3 console.
2. Select your origin bucket -> Permissions -> Bucket Policy.
3. Ensure your policy looks exactly like this (replace placeholders):

{
    "Version": "2012-10-17",
    "Statement": {
        "Sid": "AllowCloudFrontServicePrincipalReadOnly",
        "Effect": "Allow",
        "Principal": {
            "Service": "cloudfront.amazonaws.com"
        },
        "Action": "s3:GetObject",
        "Resource": "arn:aws:s3:::YOUR_BUCKET_NAME/*",
        "Condition": {
            "StringEquals": {
                "AWS:SourceArn": "arn:aws:cloudfront::YOUR_AWS_ACCOUNT_ID:distribution/YOUR_DISTRIBUTION_ID"
            }
        }
    }
}

Common Mistake: Forgetting the /* at the end of the Resource ARN. s3:GetObject is an object-level operation, not a bucket-level operation.

Step 3: Resolving KMS Encryption Failures (SSE-KMS)

If your S3 bucket forces SSE-KMS (Server-Side Encryption with AWS Key Management Service), a standard OAC bucket policy is not enough. CloudFront needs permission to decrypt the objects.

When a client requests a file, S3 attempts to decrypt it using the KMS key. If CloudFront's service principal isn't allowed to use the KMS key, S3 throws an AccessDenied error.

The Solution for KMS

Modify the KMS Key Policy (not the S3 bucket policy) to allow CloudFront to use the key:

1. Go to the AWS KMS Console.
2. Find the Customer Managed Key (CMK) used to encrypt the S3 bucket.
3. Add the following statement to the key policy:

{
    "Sid": "AllowCloudFrontToDecrypt",
    "Effect": "Allow",
    "Principal": {
        "Service": "cloudfront.amazonaws.com"
    },
    "Action": [
        "kms:Decrypt",
        "kms:GenerateDataKey*"
    ],
    "Resource": "*",
    "Condition": {
        "StringEquals": {
            "AWS:SourceArn": "arn:aws:cloudfront::YOUR_AWS_ACCOUNT_ID:distribution/YOUR_DISTRIBUTION_ID"
        }
    }
}

Note: OAI does not support SSE-KMS. If you are using KMS, you MUST use OAC.

Step 4: Missing Default Root Object

If you receive a 403 Forbidden when accessing the root domain (e.g., https://example.com/) but accessing a specific file works (e.g., https://example.com/index.html), the issue is the Default Root Object.

1. In the CloudFront console, select your distribution.
2. Click the General tab -> Settings -> Edit.
3. In the Default root object field, type index.html (or your entry point).
4. Save changes and invalidate the cache.

Step 5: Handling Single Page Applications (SPAs)

Frameworks like React, Vue, or Angular use client-side routing. If a user navigates to https://example.com/about and refreshes the page, CloudFront will request the /about object from S3. S3 doesn't have an /about file (it only has index.html), so it returns a 403 Access Denied.

The Solution for SPAs

You must configure CloudFront Custom Error Responses to rewrite 404 and 403 errors to the index.html file with a 200 OK status.

1. Go to your CloudFront distribution -> Error pages -> Create custom error response.
2. HTTP error code: 403: Forbidden
3. Customize error response: Yes
4. Response page path: /index.html
5. HTTP Response code: 200: OK
6. Repeat for HTTP error code 404: Not Found.

Step 6: WAF and Geo-Restrictions

If S3 configurations are pristine, inspect the edge layer.

• AWS WAF: Check the WAF console for the Web ACL attached to the distribution. View the Sampled requests to see if a rule (like a rate limit or managed rule group) is blocking the traffic. Blocked requests explicitly return a 403.
• Geo-Restriction: In the CloudFront console, check the Geographic restrictions tab to ensure you aren't inadvertently blocklisting the country from which you are testing.

Final Validation

After making any of these changes, always remember that CloudFront caches HTTP 403 and 404 errors by default (usually for 5 minutes).

To test your fix immediately, you must create an invalidation:

aws cloudfront create-invalidation --distribution-id YOUR_DIST_ID --paths "/*"

By systematically verifying the S3 bucket policy, KMS key policy, default root object, and edge configurations, you can rapidly diagnose and permanently resolve CloudFront Access Denied errors.